Telecommunications systems, cable television systems and data communication networks use optical networks to rapidly convey large amounts of information between remote points. In an optical network, information is conveyed in the form of optical signals through optical fibers. Optical fibers comprise thin strands of glass capable of transmitting the signals over long distances with very low loss.
Optical networks often employ wavelength division multiplexing (WDM) or dense wavelength division multiplexing (DWDM) to increase transmission capacity. In WDM and DWDM networks, a number of optical channels are carried in each fiber at disparate wavelengths. Network capacity is based on the number of wavelengths, or channels, in each fiber and the bandwidth, or size of the channels.
The topology in which WDM and DWDM networks are built plays a key role in determining the extent to which such networks are utilized. Ring topologies are common in today's networks. WDM add/drop units serve as network elements on the periphery of such optical rings. By using WDM add/drop equipment at each network element (node), the entire composite signal can be fully demultiplexed into its constituent channels and switched (added/dropped or passed through). Such add/drop equipment can be used to drop traffic off an optical ring to one or more clients associated with the add/drop equipment. In addition, add/drop equipment can be used to communicate traffic from one optical ring to another optical ring. When communicating, or adding, optical signals from one optical component to another, such as from one component to a network, interference may arise between the optical signals being added and the optical traffic already being communicated on the network.